The use of exhaust gas recirculation (EGR) techniques to reduce the amount of nitrous oxides in exhaust gas generated by an internal combustion engine is well known in the art. Generally, EGR techniques include recirculating a portion of the exhaust gas generated by a combustion event within a combustion chamber of the engine back into the combustion chamber for a future combustion event. The recirculated exhaust gas reduces the temperature of the combustion components prior to combustions. The lower temperature of the combustion components promotes a reduction in the amount of nitrous oxides generated as a result of the combustion process.
To further reduce the temperature of the combustion components and improve the reduction of nitrous oxides in the exhaust gas, EGR coolers have been employed to cool the recirculating exhaust gas prior to entering the combustion chamber. EGR coolers also enable higher EGR flow rates into the combustion chambers of the engine. The effectiveness of an EGR cooler to reduce the temperature of exhaust gas varies based on the operating conditions of the engine system. For example, EGR cooler effectiveness tends to decrease with increased EGR flow rates. In contrast, EGR cooler effectiveness tends to increase with increased exhaust gas temperatures.
Unfortunately, EGR coolers are prone to fouling (i.e., a degradation of the condition of the EGR cooler). Fouling can occur when unburned hydrocarbons (UHC) and/or particulate matter (PM) accumulate on the walls of the EGR cooler. The deposition of UHC and PM within the EGR cooler degrades the effectiveness (e.g., the heat transfer efficiency) of the EGR cooler and obstructs the flow of exhaust through the cooler. Other factors that may promote the fouling of EGR coolers includes extreme boundary conditions (e.g., extreme exhaust gas temperatures, extreme coolant temperatures, and extreme exhaust gas flow rates), frequency and duration of operating modes of the engine (e.g., steady state, transient, and shutdowns), the design of the cooler, and chemical reactions and acids forming within the cooler. Regardless of the cause, EGR fouling degrades the effectiveness of the EGR cooler to reduce the temperature of the exhaust gas, negates the advantages of increased EGR flow provided by the cooler, and creates backpressure issues within the exhaust system. Accordingly, although the effectiveness of an EGR cooler varies based on operating conditions of the engine system, the effectiveness of the cooler at each operating condition is scaled downward when the EGR cooler is fouled.
Some prior art systems attempt to model the effectiveness of an EGR cooler based on various operating conditions. While such models may provide an estimate of the effectiveness of the EGR cooler, they fail to provide any indication of the fouling or condition of the EGR cooler. Accordingly, to identify the fouling or condition of an EGR cooler, prior art techniques include physically removing the EGR cooler from the system and visually inspecting the cooler for indications of fouling. Of course, physically removing and inspecting an EGR cooler necessitates significant vehicle downtime and labor, all of which leads to increased costs and a loss in productivity.